Final answer:
In programming, 'variable-2' is usually not a valid variable name as it contains a hyphen, which is often interpreted as the subtraction operator and not allowed in variable identifiers.
Step-by-step explanation:
In programming, a variable name is an identifier assigned to a memory location to store data. The rules for naming variables can vary between programming languages, but there are some common conventions. Generally, a variable name must start with a letter (a-z, A-Z) or an underscore (_), followed by letters, digits (0-9), or underscores. Some languages also allow the use of other characters, such as dollar signs ($), but this is less common.
Given the options A. variable-2, B. variable_2, and C. variable$2, option A (variable-2) is not a valid variable name in most programming languages because it contains a hyphen (-). Hyphens are typically not allowed in variable names because they can be confused with the subtraction operator. Option C (variable$2) might be valid in some languages like Perl, but in other more commonly used programming languages like Python or Java, it would not be considered valid.